1. Field of the Invention
The present invention relates to a method for forming an oxide film in a semiconductor device, more particularly to a method for forming an oxide film, which can obtain an oxide film of good quality by growing an oxide film under environment of mixed gas of N.sub.2 O gas and NH.sub.3 gas during a main oxidation process and by using N.sub.2 O gas during a pre-oxidation process and a post-oxidation process.
2. Information Disclosure Statement
In general, in order to enhance the reliability of oxide film in a semiconductor device, nitrogen is introduced in an oxide film. In the method for forming an oxide film using NH.sub.3 gas, the long-term reliability of the oxide film is deteriorated due to hydrogen ions contained in NH.sub.3 gas. There is another method for forming an oxide film using N.sub.2 O gas, however, an high temperature process is required because of the high activation energy of N.sub.2 O gas. Also it is impossible to control independently the oxidation rate and influx of the nitrogen. That is, N.sub.2 O gas is resolved into 64.3% of N.sub.2, 31.0% of O.sub.2 gas and 4.7% of NO gas in the oxidation chamber under a temperature of 950 degree Celsius. The NO gas is needed to introduce nitrogen into the oxide film, however, NO gas exists in extremely small quantities of 4.7%. Also, most of the NO gas acts upon the O.sub.2 gas, and NO.sub.2 gas is formed according to the chemical reaction formula: (2NO+O.sub.2 =2NO.sub.2). Therefore, because the influx of nitrogen depends on the degree of reaction of NO gas and O.sub.2 gas, it is impossible to control independently the oxidation rate and influx of the nitrogen.